In a barn outside Manhattan, Kan., researchers from Kansas State University are trying to solve the riddle of bovine respiratory disease. They're sticking plastic rods down the noses of 6-month old calves, collecting samples of bacteria.

"This bacteria, Mannheimia haemolytica, lives in most cattle," explains Mike Apley, one of the research leaders. Sometimes, for reasons that aren't well understood, those bacteria make cattle sick. When that happens, or when it just seems likely to happen, cattlemen deploy antibiotics.

Apley hopes to find out, among other things, whether those antibiotics actually work as advertised. If they don't, he says, it's an easy decision to not use them. Farmers save money, and meat industry critics, who want farmers to use fewer antibiotics, are happy too. "It's a win-win for everyone."

Unfortunately, when it comes to antibiotics on the farm, it's not always a win-win. And when there's a fight, veterinarians are right in the middle of it, pushed back and forth by conflicting loyalties.

To understand those pressures, I paid a visit to veterinarian Steven Henry in Abilene, Kan. Henry is a leading swine specialist.

Pork producers rely heavily on veterinarians like Henry for advice. "They don't want to spend money on drugs if they don't need to," says Henry. "Now, you have to juxtapose that with a tremendous amount of pressure from pharmaceutical companies to move product."

Those companies aim advertising campaigns at farmers and veterinarians alike. Henry says he dismisses it, but others are influenced. As a result, farmers sometimes use more drugs than they should.

In addition, many veterinarians have a financial interest in such decisions. They resell antibiotics to farmers.

"There's some margin in there for the veterinarian, so there's some incentive for the veterinarians to sell more," says Henry.

In Denmark, the government took away that incentive in 1994; it stopped veterinarians from earning profits on such sales. The next year, antibiotic use dropped by almost 25 percent. (The Danish government also banned sales of one antibiotic that year, which may account for part of the decline.) Since then, Denmark has passed other regulations limiting antibiotic use in agriculture.

But Henry says he still trusts veterinarians, more than any regulations by government, to make sure antibiotics are used wisely. When veterinarians enter the profession, in fact, they swear an oath to protect animals and also promote public health.

But they soon develop other loyalties, too — above all to farmers, who in turn are driven by the need to earn a living.

Antibiotics can make meat production more efficient. Some drugs are used to make animals grow faster. Others reduce the risk of liver abscesses in feedlot cattle that are eating energy-rich diets of corn.

Mike Apley, the veterinarian at Kansas State, says those things matter when your clients are struggling to stay in business. "The cost of production is a reality in food animal medicine and food animal production," he says.

Critics of the meat industry, though, say using antibiotics this way is irresponsible.

Anytime antibiotics are used, it increases the likelihood that bacteria will evolve resistance to them. Such drug-resistant bacteria can migrate, raising the risk of infections that doctors can't treat as easily.

Michael Blackwell, a veterinarian and former official at the Food and Drug Administration, says it's not acceptable to increase that risk just to produce meat more cheaply. Even if there's not clear evidence of harm right now, it's unwise to wait until it's too late, "when there are literally bodies in the street."

"We have got enough science to know that we need to act," says Blackwell, who also is a leader of the Humane Society Veterinary Medical Association, and a critic of methods used by meat producers. Blackwell says antibiotics should only be used to fight disease, and only at "therapeutic" doses sufficient to kill virtually all disease-causing bacteria.

Kansas State's Mike Apley, for his part, says he's ready to stop advising meat producers to use any antibiotic if he's convinced that it could harm people. But he says the scientific evidence so far doesn't persuade him that's he's doing anything risky.

"I want to fully support human health," he says. "But at the same time, I don't want to remove valuable tools when that removal will not have a benefit for human health." He pauses. "You know, we're really ... It's tough! It's tough!"

It's tough because of scientific uncertainty, and also because veterinarians serve two masters: public health and food production.

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Transcript

STEVE INSKEEP, HOST:

Cattle and poultry farms that produce most of our hamburgers or fried chicken have been getting a lot of negative attention. Public health advocates are accusing those farms of overusing antibiotics on their animals, creating dangerous strains of drug-resistant bacteria.

The Food and Drug Administration wants to give veterinarians a bigger role in controlling antibiotic use on the farm. But as NPR's Dan Charles reports, vets themselves have conflicting loyalties.

(SOUNDBITE OF BANGING)

DAN CHARLES, BYLINE: In a barn outside Manhattan, Kansas, researchers from Kansas State University are trying to solve the riddle of bovine respiratory disease.

MIKE APLEY: This bacteria - Mannheimia haemolytica - lives in most of the cattle.

CHARLES: Mike Apley is one of the researchers here.

APLEY: It's in their nose. It's down where our tonsils would be.

CHARLES: Sometimes, those bacteria make cattle sick. So when cattlemen think animals are at risk of getting sick, they'll sometimes use antibiotics to prevent an outbreak. Apley and his colleagues are monitoring these cattle to find out, among other things, do the antibiotics actually help?

APLEY: To me, that's the next real area of research we need to focus on - is the prevention and control uses that are legal to use out there today, which ones are still actually giving us that benefit? If they're not, easy decision.

CHARLES: But decisions about antibiotics are not always a win-win. And when there's a conflict, veterinarians are right in the middle of it. I met veterinarian Steven Henry in Abilene, Kansas, the day after he got back from a long trip visiting Midwestern pork producers. Most farmers who raise animals rely on veterinarians like him for advice.

DR. STEVEN HENRY: They don't want to spend the money on the drugs, if they don't need to. This stuff's expensive. Now, you have to juxtapose that with a tremendous amount of pressure from pharmaceutical companies to move product.

CHARLES: The companies aim ad campaigns at farmers and veterinarians. Henry says that marketing does work. Farmers sometime use more drugs than they should. And veterinarians themselves may have a financial interest in such decisions. Many of them re-sell antibiotics to farmers.

HENRY: There's some margin in there for the veterinarians. So there's some incentive for the veterinarians to sell more.

CHARLES: In Denmark, the government took away that incentive; it stopped veterinarians from earning money by selling antibiotics, in 1994. The next year, antibiotic use in Denmark dropped sharply. Later, Denmark passed other regulations strictly limiting antibiotic use in agriculture.

But as Steven Henry and I drive away from his office, he says despite all that, "I would still trust veterinarians more than regulation, to make sure antibiotics are used wisely."

HENRY: Tremendously greater faith in veterinarians, who are at the animal's side, care for the animals; know the people, work with the people; tremendously more confidence there in proper use, than anything the government even hopes to do.

CHARLES: When veterinarians enter their profession, they swear an oath to protect animals and also to promote public health. But they soon develop other loyalties, too - above all, to farmers, who have to earn money.

Antibiotics can make meat production more efficient. They can make animals grow faster, or reduce the risk of liver abscesses in feedlot cattle that are eating energy-rich diets of corn.Mike Apley, the veterinarian at Kansas State, says those things matter when your clients are struggling to stay in business.

APLEY: Cost of production is a reality in food-animal medicine and food-animal production.

CHARLES: Critics of the meat industry, though, say using antibiotics this way is irresponsible. Anytime antibiotics are used, it increases the chances that bacteria will evolve resistance to them. That raises the risk of future infections that doctors can't treat as easily.

Michael Blackwell, a veterinarian and former official at the Food and Drug Administration, says it's not acceptable to take that risk just to produce meat more cheaply. We may not see clear evidence of harm now, he says, but we shouldn't wait until we do.

DR. MICHAEL BLACKWELL: It has been said, back when I was in the agency, sometimes actions cannot be taken until there are, literally, bodies in the street.

CHARLES: Blackwell is a leader of the Humane Society Veterinary Medical Association, and a critic of methods used by large meat producers. He says the government should stop farmers from using antibiotics for anything but fighting disease.

BLACKWELL: We've got enough science to know that we need to act.

CHARLES: Kansas State's Mike Apley, for his part, says the government should stop any antibiotic use if there's solid evidence it could harm people. But he says the scientific evidence so far doesn't persuade him that's he's doing anything risky.

APLEY: I want to fully support human health but at the same time, I don't want to remove valuable tools when that removal will not have a benefit for human health. You know, we're really - it's tough. It's tough.

CHARLES: It's tough because of scientific uncertainty, but also because veterinarians serve two masters: public health and food production.